Various types of programmed valves are already known and these are used to automate hydraulic systems, opening and closing the system in order to allow the fluid to pass thru without direct manual intervention at the time the operation takes place and allowing the fluid to be distributed automatically and successively from several valves fitted to the pipe, with electric pulses or hydraulic pulses in a hydraulic supply system, or a mixture, or pulses programmed from complex and delicate equipment. The commands are conveyed to the valve by means of electric or hydraulic lines.
Also known are valves whichprogram the sequence by which they open and close by controlling the flow, a new command being received every time a variation in the pressure of the fluid upstream of the valve itself is detected; each time, the sequence of pulses causes one or more valves, which are different from those that opened previously and from those that will open subsequently, to open. These valves do not distinguish between the variations produced deliberately and those which occur accidentally as a result of the conditions in the hydraulic system to which they are connected, so that there is little reliability as regards the desired sequence of opening and closing and an irrigation program--for example--may therefore be altered.